This invention relates to the field of optical information processing and, more particularly, to amplitude and phase response measurements of an optical component.
Optical data processing systems have several advantages over electronic systems, such as, speed, dynamic range, resolution and reliability. Interest in such systems has increased recently due in part to the advances being made in the materials used to manufacture the optical components of the systems. For purposes of designing an optical data processing system, there is a need to determine quantitatively how an optical component modulates, in both amplitude and phase, a coherent beam of light transmitted or reflected by the optical component. In particular, there is a need to determine the amplitude and phase of a laser beam that has been modulated by a spatial light modulator (SLM) when it is used to convert an incoherent, "writing" light signal to a coherent, "reading" light pattern.
Amplitude characteristics are usually derived from relative intensity measurements, (for example, an "H-D" curve). Interferometric methods are used traditionally to observe the changes in phase of a coherent light beam when the beam is reflected or transmitted through an optical component. When using an interferometric system, phase changes are observed as light-to-dark fringe patterns which are due to constructive and destructive interference of the combined light beams. These methods are well known to those skilled in the field of optics.
The use of any one of several conventional interferometric methods to measure quantitatively the phase of an optical component is very time consuming and tedious even if automated. Furthermore, the phase must be calculated from the light intensity measurements of the fringe pattern maximum and minimum levels within the pattern itself. If S= measured value of light intensity, S.sub.MAX, S.sub.MIN = maximum and minimum values of S, and .phi.=optical phase,
then, ##EQU1## .phi. is calculated from measured values of S, S.sub.MAX and S.sub.MIN.
To map the phase and amplitude across the face of the optical component, a detector with a small aperture moving transverse to the output beam can be used. This is obviously a slow process when relatively large areas are to be evaluated. There is an additional complication when testing an SLM. Since the amplitude and phase response of an SLM will change with changes in the input, "writing", light intensity, a conventional interferometric method to measure phase .phi. would be very impractical to use. It is important to note that in this application, the amplitude response will alter the values of S.sub.MAX and S.sub.MIN so that these quantities must be determined for each input "write" light level used.